Structure of strained silicon on insulator and method of manufacturing the same

ABSTRACT

Provided is a strained SOI structure and a method of manufacturing the strained SOI structure. The strained SOI structure includes an insulating substrate, a SiO 2  layer formed on the insulating substrate, and a strained silicon layer formed on the SiO 2  layer.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

Priority is claimed to Korean Patent Application No. 10-2004-00103111,filed on Dec. 8, 2004, in the Korean Intellectual Property Office, thedisclosure of which is incorporated herein in its entirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a strained silicon on insulator(strained SOI) structure and a method of manufacturing the same, andmore particularly, to a strained SOI structure having a small parasiticcapacitance and high carrier mobility and a method of manufacturing thesame.

2. Description of the Related Art

A strained silicon CMOS is a CMOS device that includes a thin, strainedsilicon layer on a relaxed SiGe layer. The mobility of electrons andholes within the strained silicon layer is known to be much higher thanwith a bulk silicon layer, and devices manufactured using a MOFET havinga strained silicon channel have improved device performances compared todevices manufactured using a conventional (unstrained silicon) siliconsubstrate. The potential performance improvement of devices increasesdevice driving current and mutual conductance and reduces powerconsumption.

The formation of the strained silicon layer is the result of tensilestrain occurs on silicon grown on a substrate formed of a materialhaving a greater lattice constant than the lattice constant of thesilicon. The lattice constant of germanium Ge is approximately 4.2 whichis greater than the lattice constant of silicon, and the latticeconstant of silicon-germanium SiGe is linear to the concentration ofgermanium Ge. That is, the lattice constant of SiGe that contains 50% Geis 1.02 times greater than the lattice constant of silicon. Theepitaxial growth of silicon on a SiGe substrate generates the tensilestrain of a silicon layer, and the SiGe substrate underneath the siliconlayer is in a non-strained or relaxed state.

A method of forming a CMOS device having a strained silicon channel on aSiGe layer formed on an insulating substrate is disclosed in U.S. Pat.No. 6,059,895.

The difficulty in implementing the advantages of the strained siliconCMOS technique is the presence of a relaxed SiGe layer underneath thestrained silicon layer. The SiGe layer interacts with the strainedsilicon layer in the processes of thermal oxidation, forming silicide,and annealing. Therefore, the improvement of device performance and adevice yield that can be achieved may be limited during manufacturing aCMOS due to the difficulty of maintaining an integrity of material.Another disadvantage is that the thickness of the SiGe layer is added tothe total thickness of a MOSFET main body. The addition of a thicknessto the MOSFET is especially undesirable to the SOIFET structure sincethe additional thickness affects adversely to the super slim SOI devicein which a MOSFET structure having a very thin channel is included.

SUMMARY OF THE INVENTION

The present invention provides a strained silicon on insulator (strainedSOI) structure having a small parasitic capacitance and high carriermobility and a method of manufacturing the same.

According to an aspect of the present invention, there is provided astrained SOI structure comprising: an insulating substrate; a SiO₂ layerformed on the insulating substrate; and a strained silicon layer formedon the SiO₂ layer.

The strained SOI structure can further comprise a bonding layer betweenthe insulating substrate and the SiO₂ layer, and the bonding layer canbe formed one of SiO₂ and polycrystalline silicon.

The insulating substrate can be a substrate selected from the groupconsisting of a glass substrate, a plastic substrate, and a Si substrateon which an oxide layer is formed. The strained SOI structure canfurther comprise a protective layer that surrounds the insulatingsubstrate and the protective layer can be formed of AIN.

According to another aspect of the present invention, there is provideda method of manufacturing a strained SOI structure, comprising:preparing a Si substrate and an insulating substrate; forming a poroussilicon layer by anodizing a predetermined thickness of the Sisubstrate; forming a SiGe layer on the porous silicon layer; forming astrained silicon layer on the SiGe layer; forming a SiO₂ layer on thestrained silicon layer; activating a surface of the SiO₂ layer bytreating the surface of the SiO₂ layer using oxygen O₂ plasma; bondingthe insulating substrate on the activated SiO₂ layer; removing the SiGelayer by selectively etching after reversing the stacked structure sothat the insulating substrate is placed on a lower position; andseparating the porous silicon layer and the Si substrate from thestrained silicon layer.

According to another aspect of the present invention, there is provideda method of manufacturing a strained SOI structure, comprising:preparing a Si substrate and an insulating substrate; forming a SiGelayer on the Si substrate; forming a porous SiGe layer by anodizing apredetermined thickness of the SiGe layer; forming a strained siliconlayer on the porous SiGe layer; forming a SiO₂ layer on the strainedsilicon layer; activating a surface of the SiO₂ layer by treating thesurface of the SiO₂ layer using oxygen O₂ plasma; bonding the insulatingsubstrate on the activated SiO₂ layer; removing the porous SiGe layer byselectively etching after reversing the stacked structure so that theinsulating substrate is placed on a lower position; and separating theSi substrate from the strained silicon layer.

The insulating substrate can be a substrate selected from the groupconsisting of a glass substrate, a plastic substrate, and a Si substrateon which an oxide layer is formed.

The preparing of the insulating substrate can include preparing aninsulating substrate and forming a protective layer on a surface of theinsulating substrate. Here, the protective layer is formed of AIN.

The preparing of the insulating substrate can include preparing aninsulating substrate, forming a protective layer on a surface of theinsulating substrate, and forming a bonding layer on the protectivelayer. Here, the bonding layer can be formed one of SiO₂ andpolycrystalline silicon.

According to another aspect of the present invention, there is provideda method of manufacturing a strained SOI structure, comprising:preparing a Si substrate and an insulating substrate; forming a SiO₂layer on the Si substrate; forming at least two SiO₂ barrier ribs spaceda predetermined distance from each other by patterning the SiO₂ layer;forming a SiGe layer on the Si substrate between the two barrier ribs;forming a strained silicon layer on the SiGe layer; removing the SiO₂barrier ribs; bonding the insulating substrate on the strained siliconlayer; removing the SiGe layer by selectively etching after reversingthe stacked structure so that the insulating substrate is placed on alower position; and separating the Si substrate from the strainedsilicon layer.

The insulating substrate can be a substrate selected from the groupconsisting of a glass substrate, a plastic substrate, and a Si substrateon which an oxide layer is formed.

The preparing of the insulating substrate can include preparing aninsulating substrate and forming a protective layer on a surface of theinsulating substrate. Here, the protective layer is formed of AIN.

The preparing of the insulating substrate can include preparing aninsulating substrate, forming a protective layer on a surface of theinsulating substrate, and forming a bonding layer on the protectivelayer.

Here, the bonding of the insulating substrate on the strained siliconlayer can includes activating a surface of the bonding layer by treatingusing oxygen O₂ plasma and bonding the insulating substrate on thestrained silicon layer. The bonding layer can be formed one of SiO₂ andpolycrystalline silicon.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present inventionwill become more apparent by describing in detail exemplary embodimentsthereof with reference to the attached drawings in which:

FIG. 1 is a cross-sectional view of a strained SOI structure accordingto an embodiment of the present invention;

FIGS. 2A through 2L are cross-sectional views illustrating a method ofmanufacturing a strained SOI structure according to a first embodimentof the present invention;

FIGS. 3A through 3L are cross-sectional views illustrating a method ofmanufacturing a strained SOI structure according to a second embodimentof the present invention; and

FIGS. 4A through 4L are cross-sectional views illustrating a method ofmanufacturing a strained SOI structure according to a third embodimentof the present invention.

DETAILED DESCRIPTION OF THE INVENTION

A strained SOI structure and a method of manufacturing the strained SOIstructure will now be described more fully with reference to theaccompanying drawings in which exemplary embodiments of the inventionare shown.

FIG. 1 is a cross-sectional view of a strained SOI structure accordingto an embodiment of the present invention.

Referring to FIG. 1, a protective layer 12 that surround an insulatingsubstrate 10, a bonding layer 14 formed on the protective layer 12, aSiO₂ layer 28, and a strained silicon layer 26 are sequentially formedon the insulating substrate 10. The protective layer 12 and the bondinglayer 14 are not requisite layers.

The insulating substrate 10 is a substrate selected from the groupconsisting of a glass substrate, a plastic substrate, and an oxidelayer. Also, the protective layer 12 is formed of a material havingcharacteristics of insulating, transparent, and resisting to an etchant,such as AIN. The bonding layer 14 is formed of SiO₂ or polycrystallinesilicon.

A strained SOI structure formed on the insulating substrate 10 has highperformance, small parasitic capacitance, and high carrier mobility.Especially, the strained SOI structure can be applied to a front panelor a rear panel of a display panel by using a plastic substrate or aglass substrate as the insulating substrate 10.

FIGS. 2A through 2L are cross-sectional views illustrating a method ofmanufacturing a strained SOI structure according to a first embodimentof the present invention. Here, like reference numerals refer to likeelements throughout the drawings. The formation of material layersduring the processes is formed using a well known thin film depositionapparatus such as ultra high vacuum chemical vapor deposition (UHV-CVD)or low pressure chemical vapor deposition (LPCVD).

Referring to FIGS. 2A through 2C, a protective layer 12 is formed on asurface of an insulating substrate 10. The protective layer 12 is formedof a material having characteristics of insulating, transparent, andresistance to an etchant, such as AIN. Next, a bonding layer 14 formedof a material, such as SiO₂ or polycrystalline silicon, is formed on theprotective layer 12. Here, the protective layer 12 and the bonding layer14 are not requisite layers.

Referring to FIGS. 2D through 2H, after preparing a Si substrate 20, aporous silicon layer 22 is formed by anodizing a predetermined thicknessof the Si substrate 20. To form the porous silicon layer 22, apredetermined thickness of the Si substrate 20 is anodizedelectrochemically in a mixed solution of fluoride hydrogen HF andethanol.

Afterward, a SiGe layer 24, a strained silicon layer 26, and a SiO₂layer 28 are sequentially formed on the porous silicon layer 22. Here,the SiGe layer 24 has a relaxed structure. Accordingly, the strainedsilicon layer 26 can be formed on the SiGe layer 24.

Referring to FIGS. 21 through 2L, a surface of the SiO₂ layer 28 isactivated by treating the surface using oxygen O₂ plasma. Next, theprepared insulating substrate 10 is bonded on the activated SiO₂ layer28. Here, a surface of the bonding layer 14 formed on the insulatingsubstrate 10 can be activated by treating the surface using oxygen O₂plasma prior to bond the insulating substrate 10.

Next, the stacked structure is reversed so that the insulating substrate10 can be placed in a lower position. Next, the SiGe layer 24 is removedby selective etching. Here, an etchant for selectively etching the SiGelayer 24 is a mixed solution of 50% HF:60% HNO₃:H₂O=1:90˜120:60. Otheretchants that can selectively etch the SiGe layer 24 can also be used.Here, the etchant readily reacts with the SiGe layer 24 not only on bothside surfaces but also through the porous silicon layer 22 by beingabsorbed by the porous silicon layer 22.

The porous silicon layer 22 and the Si substrate 20 formed on the SiGelayer 24 can be separated from the strained silicon layer 26 byselectively removing the SiGe layer 24. As a result, as depicted in FIG.2L, a strained SOI structure formed on the insulating substrate 10 canbe obtained.

FIGS. 3A through 3L are cross-sectional views illustrating a method ofmanufacturing a strained SOI structure according to a second embodimentof the present invention. Here, like reference numerals refer to likeelements throughout the drawings. The formation of material layersduring the processes is formed using a well known thin film depositionapparatus such as UHV-CVD or LPCVD.

Referring FIGS. 3A through 3C, after preparing an insulating substrate10, a protective layer 12 is formed on the insulating substrate 10. Theprotective layer 12 is formed of a material having characteristics ofinsulating, transparent, and resistance to an etchant, such as AIN. Abonding layer 14 formed of SiO2 or polycrystalline silicon is formed onthe protective layer 12. The protective layer 12 and the bonding layer14 are not requisite.

Referring to FIGS. 3D through 3H, after preparing the Si substrate 20, aSiGe layer 24 having a predetermined thickness is formed on the Sisubstrate 20. Here, the SiGe layer 24 has a relaxed structure. Next, aporous SiGe layer 25 is formed by anodizing the SiGe layer 24. To formthe porous SiGe layer 25, a predetermined thickness of the porous SiGelayer 25 is anodized electrochemically in a mixed solution of fluoridehydrogen HF and ethanol.

Next, the strained silicon layer 26 and the SiO₂ layer 28 aresequentially formed on the porous SiGe layer 25.

Referring to FIGS. 31 through 3L, a surface of the SiO₂ layer 28 isactivated by treating the surface using oxygen O₂ plasma. Next, theprepared insulating substrate 10 is bonded on the activated SiO₂ layer28. Here, a surface of the bonding layer 14 formed on the insulatingsubstrate 10 can be activated by treating the surface using oxygen O₂plasma prior to bond the insulating substrate 10.

Next, the stacked structure is reversed so that the insulating substrate10 can be placed in a lower position. Next, the porous SiGe layer 25 isremoved by selective etching. Here, an etchant for selectively etchingthe porous SiGe layer 25 is a mixed solution of 50% HF:60%HNO₃:H₂O=1:90˜120:60. Other etchants that can selectively etch theporous SiGe layer 25 can also be used. Here, the etchant readily reactswith the porous SiGe layer 25 by being absorbed by the porous SiGe layer25.

The Si substrate 20 formed on the porous SiGe layer 25 can be separatedfrom the strained silicon layer 26 by selectively removing the porousSiGe layer 25. As a result, as depicted in FIG. 3L, a strained SOIstructure formed on the insulating substrate 10 can be obtained.

FIGS. 4A through 4L are cross-sectional views illustrating a method ofmanufacturing a strained SOI structure according to a third embodimentof the present invention. Here, like reference numerals refer to likeelements throughout the drawings. The formation of material layersduring the processes is formed using a well known thin film depositionapparatus such as UHV-CVD or LPCVD.

Referring FIGS. 4A through 4C, after preparing the insulating substrate10, the protective layer 12 is formed on the insulating substrate 10.The protective layer 12 is formed of a material having characteristicsof insulating, transparent, and resistance to an etchant, such as AIN.The bonding layer 14 formed of SiO₂ or polycrystalline silicon is formedon the protective layer 12. The protective layer 12 and the bondinglayer 14 are not requisite.

Referring to FIGS. 4D through 4H, after preparing the Si substrate 20, aSiO₂ layer 21 having a predetermined thickness is formed on the Sisubstrate 20. At least two SiO₂ barrier ribs 23 spaced a predetermineddistance from each other are formed by patterning the SiO₂ layer 21. ASiGe layer 24 and a strained silicon layer 26 are sequentially formed onthe Si substrate 20 between the two SiO₂ barrier ribs 23. Here, the SiGelayer 24 has a relaxed structure. Accordingly, the strained siliconlayer 26 can be formed on the SiGe layer 24. Afterward, the SiO₂ barrierribs 23 are removed.

Referring to FIGS. 41 through 4L, a surface of the bonding layer 14formed on the insulating substrate 10 is activated by treating thesurface using oxygen O₂ plasma. Next, the insulating substrate 10 isbonded on the strained silicon layer 26 formed on the Si substrate 20.

Next, the stacked structure is reversed so that the insulating substrate10 can be placed in a lower position. Next, the SiGe layer 24 is removedby selective etching. Here, an etchant for selectively etching the SiGelayer 24 is a mixed solution of 50% HF:60% HNO₃:H₂O=1:90˜120:60. Otheretchants that can selectively etch the SiGe layer 24 can also be used.

The Si substrate 20 formed on the SiGe layer 24 can be separated fromthe strained silicon layer 26 by selectively removing the SiGe layer 24.As a result, as depicted in FIG. 4L, a strained SOI structure formed onthe insulating substrate 10 can be obtained.

The method of manufacturing a strained SOI structure according toembodiments of the present invention can readily form the strained SOIstructure on an insulating substrate since the process for separatingthe substrate is as simple as that the SiGe layer can be removed byselective etching after a bonding process. Also, the method ofmanufacturing a strained SOI structure can use conventionalmanufacturing facilities without additional cost for equipment.Especially, the strained SOI structure can be formed on a substrate suchas a plastic substrate or a glass substrate, which is weak to heat,since the method does not include an annealing process at a temperaturehigher than a conventional temperature of 1100° C. The strained SOIstructure can be applied to a front substrate or a rear substrate of adisplay panel.

According to the present invention, a strained SOI structure formed onan insulating substrate such as a plastic substrate, a glass substrate,or a Si substrate on which an oxide layer is formed is provided. Thestrained SOI structure formed on the insulating substrate has highperformance, a small parasite capacitance, and high carrier mobility.Also, the strained SOI structure can be applied to memory devices andsemiconductor devices for next generation.

While the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the present invention as defined by the following claims.

1. A method of manufacturing a strained SOI structure, comprising: preparing a Si substrate and an insulating substrate; forming a SiGe layer on the Si substrate; forming a porous SiGe layer by anodizing a predetermined thickness of the SiGe layer; forming a strained silicon layer on the porous SiGe layer; forming a SiO₂ layer on the strained silicon layer; activating a surface of the SiO₂ layer by treating the surface of the SiO₂ layer using oxygen O₂ plasma; bonding the insulating substrate on the activated SiO₂ layer; removing the porous SiGe layer by selectively etching; and separating the Si substrate from the strained silicon layer.
 2. The method of claim 1, wherein the insulating substrate is a substrate selected from the group consisting of a glass substrate, a plastic substrate, and a Si substrate on which an oxide layer is formed.
 3. The method of claim 1, wherein the preparing of the insulating substrate includes: preparing an insulating substrate; and forming a protective layer on a surface of the insulating substrate.
 4. The method of claim 4, wherein the protective layer is formed of AIN.
 5. The method of claim 1, wherein the preparing of the insulating substrate includes: preparing an insulating substrate; forming a protective layer on a surface of the insulating substrate; and forming a bonding layer on the protective layer.
 6. The method of claim 5, wherein the bonding layer is formed one of SiO₂ and polycrystalline silicon.
 7. A method of manufacturing a strained SOI structure, comprising: preparing a Si substrate and an insulating substrate; forming a SiO₂ layer on the Si substrate; forming at least two SiO₂ barrier ribs spaced a predetermined distance from each other by patterning the SiO₂ layer; forming a SiGe layer on the Si substrate between the two barrier ribs; forming a strained silicon layer on the SiGe layer; removing the SiO₂ barrier ribs; bonding the insulating substrate on the strained silicon layer; removing the SiGe layer by selectively etching; and separating the Si substrate from the strained silicon layer.
 8. The method of claim 7, wherein the insulating substrate is a substrate selected from the group consisting of a glass substrate, a plastic substrate, and a Si substrate on which an oxide layer is formed.
 9. The method of claim 7, wherein the preparing of the insulating substrate includes: preparing an insulating substrate; and forming a protective layer on a surface of the insulating substrate.
 10. The method of claim 9, wherein the protective layer is formed of AIN.
 11. The method of claim 7, wherein the preparing of the insulating substrate includes: preparing an insulating substrate; forming a protective layer on a surface of the insulating substrate; and forming a bonding layer on the protective layer.
 12. The method of claim 11, wherein the bonding of the insulating substrate on the strained silicon layer includes: activating a surface of the bonding layer by treating using oxygen O₂ plasma; and bonding the insulating substrate on the strained silicon layer.
 13. The method of claim 12, wherein the bonding layer is formed one of SiO₂ and polycrystalline silicon. 